The present invention relates to an exposing apparatus and an exposing method for a microlens array used in a liquid crystal panel and the like.
Projection-type liquid crystal display apparatuses have advantages over projection-type cathode-ray tube display apparatuses in that the projection-type liquid crystal apparatuses have a wider color reproduction range, are highly portable because of their small size and light weight, and require no convergence adjustment because the projection-type liquid crystal apparatuses are not influenced by earth magnetism. Moreover, larger screens can easily be attained in the projection-type liquid crystal apparatuses. Therefore, the projection-type liquid crystal apparatuses are expected to be a mainstream of future home image display apparatuses.
There are two types of projection-type color image display systems using liquid crystal display elements: a three-plate system, in which three plates of liquid crystal display element are respectively used for three primary colors; and a single-plate system, in which only a single plate is used. The three-plate system uses an optical system and three plates of liquid crystal display element. The optical system divides white light into three primary colors of R, G, and B. The three plates of liquid crystal display element form images by respectively controlling the light of three primary colors. The images of the three primary colors are then optically superimposed, so as to perform full-color display.
Advantages of the three-plate system are that the light emitted from a white light source can be effectively utilized, and that color purity is high. However, the three-plate system requires a color separating system and a color combining system, as described above. This causes the optical system to be complex, because a large number of parts are required. As a result, it is difficult to attain miniaturization and low cost.
On the other hand, the single-plate system uses only a single plate of liquid crystal display element. In the single-plate system, light is projected on the single plate of liquid crystal display element, which includes a three-primary-color color filter pattern of a mosaic-shape, stripe-shape, or the like, using a projecting optical system. The single-panel system is suitable for low-cost and small-sized projector systems, because only a single plate of liquid crystal display element is used, and because the arrangement of the optical system is simpler than that of the three-panel system.
However, in the single-panel system, the light is absorbed or reflected by the color filter. As a result, only approximately one-third of incident light can be utilized. To overcome this drawback, a color-filter-less liquid crystal display apparatus of a single-panel system using bilayered microlens array has been proposed (see, for example, Japanese Publication for Unexamined Patent Application No. 181487/1995 (Tokukaihei 7-181487; publication date: Jul. 21, 1995), a Japanese equivalent to the U.S. Pat. No. 5,633,737).
In this apparatus, the white light emitted from a white light source is divided into colors of R, G, and B by a dichroic mirror disposed in a sector form. Then, the light of three primary colors are respectively incident at different angles on a microlens array disposed on the light-source-side of a liquid crystal display element. Each light beam transmitted through the first microlens array is then refracted by the second microlens array, so that the key light of R, G, and B, which have been produced by the dichroic mirror, become substantially parallel. Then, the refracted light beams are projected onto portions of the liquid crystal to be driven by signal electrodes, to which color signals respectively corresponding to the key light of R, G, and B are applied respectively.
In this apparatus, no absorber-type color filter is used. Therefore, light is more efficiently utilized. Besides, since the key light beams of R, G, and B are substantially parallel, the key light beams of R, G, and B do not spread significantly before reaching a projection lens. Moreover, it is possible to provide a very bright image because an amount of light does not decrease through the projection lens.
Here, the second microlens needs to have a large refracting power in order to deflect the key light of G and B parallel to the key light of R. The second microlens is therefore thick, and pixels are arranged in a mosaic-shape. Further, a vertical wall needs to be provided, which causes a problem of proportional decrease in light efficiency when there is a tilt in the vertical wall. No specific manufacturing method or exposing method is disclosed.
With regard to a method for fabricating a bilayered microlens array, there has been proposed a method in which a first layer is formed by 2P molding, and a second layer is molded using the same stamper mold that is used for the first layer and using a material whose refractive index is different from that of the material used for the first layer (see, for example, Japanese Publication for Unexamined Patent Application No. 98102/2000 (Tokukai 2000-98102; publication date: Apr. 7, 2000)).
However, the method for fabricating a bilayered microlens array has the following problem. In performing molding, the stamper mold is moved up and down using a bearing having excellent straightness. Here, the accuracy of alignment between the first microlens and the second microlens in an in-plane direction depends on the accuracy of the bearing. Therefore, it is difficult to meet a required specification, i.e., to keep the accuracy of alignment within xc2x110% from the pixel pitch. If misalignment occurs beyond this range, the light efficiency drastically decreases. Besides, a light beam enters an adjacent pixel. As a result, a so-called color mixture is caused, thereby drastically impairing image quality.
In order to minimize misalignment, it is necessary to mold the second microlens with the substrate and the stamper mold held in place in the apparatus after molding the first microlens. Because of this, the first microlens and the second microlens have the same shape. That is, freedom of design necessary for attaining optimal light efficiency is not present. Therefore, the shapes disclosed in Tokukaihei 7-181487 cannot be formed. As a result, sufficient properties cannot be attained.
Moreover, the refractive index of the second microlens needs to be larger than that of the first microlens, and the refractive index of the substrate needs to be larger than that of the second microlens. However, the refractive index of the UV resin can vary only within a limited range. Therefore, the refractive indices on the respective lens surfaces cannot differ by a sufficient margin. As a result, lenses having a short focal length cannot be fabricated.
In addition, in a method using a mold, such as the 2P method or an injection molding method, the formation of the vertical wall poses difficulties in molding, and even when the vertical wall is successfully formed, the method causes damage on a lens portion when the microlens array is detached from the mold. There has been no exposing apparatus that can solve these problems.
The present invention was made to solve the problems above. An object of the present invention is to provide an exposing apparatus for a microlens array that allows for easy alignment and attains high accuracy, and to provide an exposing method for a microlens array that attains high accuracy and high light efficiency.
To solve the problems above, in the present invention, an exposing apparatus for a microlens array includes: a secondary point light source generating section for converting a light beam from a light source into secondary point light sources; a luminance adjustment section for receiving light of each secondary point light source and adjusting luminance of the light; and a parallel light beam generating section for converting the light with adjusted luminance into a parallel light beam, and guiding the parallel light beam, via a first microlens array which is formed in advance, to a photosensitive resin layer to be a second microlens array.
According to the invention, the light beam from the light source is incident on the secondary point light source generating section, and is converted into secondary point light sources. The light beams of the respective secondary point light sources are incident on the luminance adjustment section, and the luminances of the respective light beams are adjusted therein. With this arrangement, the point light sources function as point light sources having variable luminances. Therefore, it is possible to adjust the luminances of the light beams incident on the photosensitive resin layer.
The light of adjusted luminance is incident on the parallel light beam generating section, and is converted into parallel light beams therein. The light converted into parallel light beams is incident on the first microlens array, which is formed in advance, and is refracted, condensed, and guided to the photosensitive resin layer. In this way, the photosensitive resin layer is exposed with high accuracy. By thus exposing the photosensitive resin layer, the second microlens array is formed.
The incident angles of the light guided from the parallel light beam generating section to the second microlens array depend on the position of the secondary point light source emitted by the secondary point light source generating section. The illuminance of each parallel light beam on the second microlens array (illuminance of the parallel light beam on the photosensitive resin layer) can be varied by the adjustment by the luminance adjustment section.
With this arrangement, the second microlens array can be fabricated with high accuracy, without requiring a conventional complex alignment step, in which the first microlens and the second microlens are aligned in the in-plane direction by moving a stamper mold up and down using a bearing in performing molding. This drastically improves light efficiency of the microlens array. Moreover, this prevents the color mixture that occurs when the light beam enters an adjacent pixel. As a result, image quality is drastically improved.
Moreover, designing of the microlens array is no longer restricted by the alignment step, because the illuminances on the photosensitive resin layer are adjusted by the luminance adjustment section. Therefore, freedom of design, which is necessary to optimize light efficiency, can be drastically improved. In addition, the refractive indices on the respective lens surfaces can differ by a sufficient margin. As a result, it is possible to fabricate lenses having a short focal length. Furthermore, the formation of the vertical wall is no longer required, because the conventional mold-processing is no longer required. As a result, it is possible to successfully overcome the conventional problem that the lens section is damaged when detached from the mold.
To solve the problems above, in the present invention, an exposing method for a microlens array includes the steps of: (1) converting a light beam having substantially uniform radiant intensity into secondary point light sources; (2) adjusting a luminance of light of the secondary point light source, so that the luminance matches a shape of the microlens array to be formed; and (3) converting the light of the secondary point light source into a parallel light beam, the parallel light beam passing through the microlens array to expose a photosensitive resin layer.
According to the method, the luminances of the light beams of the respective secondary point light sources are adjusted. Therefore, the point light sources function as point light sources having variable luminances. As a result, it is possible to desirably adjust the luminances of the light beams projected on the photosensitive resin layer.
The light of adjusted luminance is converted into parallel light beams. Then, the parallel light beams are refracted and condensed, and are guided to the photosensitive resin layer to be the microlens array. In this way, the photosensitive resin layer is exposed with high accuracy.
The incident angle of the parallel light beam into the microlens array depends on the position of the secondary point light source. The illuminance of the parallel light beam on the microlens array (illuminance of the parallel light beam incident on the photosensitive resin layer) can be varied by adjusting the luminance.
With this arrangement, the second microlens array can be fabricated with high accuracy, without requiring a conventional complex alignment step, in which the first microlens and the second microlens are aligned in the in-plane direction by moving a stamper mold up and down using a bearing in performing molding. This drastically improves light efficiency of the microlens array. Moreover, this prevents the color mixture that occurs when the light beam enters an adjacent pixel. As a result, image quality is drastically improved.
Moreover, designing of the microlens array is no longer restricted by the alignment step, because the illuminances on the photosensitive resin layer are adjusted by the luminance adjustment section. Therefore, freedom of design, which is necessary to optimize light efficiency, can be drastically improved. In addition, the refractive indices on the respective lens surfaces can differ by a sufficient margin. As a result, it is possible to fabricate lenses having a short focal length. Furthermore, the formation of the vertical wall is no longer required, because the conventional mold-processing is no longer required. As a result, it is possible to successfully overcome the conventional problem that the lens section is damaged when detached from the mold.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.